img{
    display: block;
    width: 250px;
    height: 156px;
    animation:myfirst 20s infinite;
    -webkit-animation:myfirst 20s infinite; /* Safari 和 Chrome */
    position: absolute;;
    top: 0;
    left: 0;
}

@keyframes myfirst
{
from {top: 0;left: 0;}
to {top: 430px;left: 1080px;}
}

@-moz-keyframes myfirst /* Firefox */
{
from {top: 0;left: 0;}
to {top: 430px;left: 800px;}
}

@-webkit-keyframes myfirst /* Safari 和 Chrome */
{
from {top: 0;left: 0;}
to {top: 430px;left: 800px;}
}

@-o-keyframes myfirst /* Opera */
{
from {top: 0;left: 0;}
to {top: 430px;left: 800px;}
}